Preparation of beryllium hydride

ABSTRACT

THIS INVENTION RELATES TO A PROCESS WHEREIN BERYLLIUM ALKYL IS PYROLYZED IN THE VAPOR PHASE TO PRODUCE BERYLLIUM HYDRIDE OF HIGH PURITY.

United States Patent 3,743,710 PREPARATION OF BERYLLIUM HYDRIDE James M. Wood, Jr., Baton Rouge, La., assignor to Ethyl Corporation, New York, N.Y. No Drawing. Filed June 7, 1965, Ser. No. 462,788 Int. Cl. C01b 6/00 U.S. Cl. 423-645 14 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a process wherein a beryllium alkyl is pyrolyzed in the vapor phase to produce beryllium hydride of high purity.

A number of methods have been disclosed for the synthesis of beryllium hydride. For example, it has been prepared by Coates and Glockling (J. Chem. Soc., 2526 (1954)) by the pyrolysis of ditertiary butyl beryllium etherate and by Head, Holley and Rabideau (J. Am. Chem. Soc. 79, 3687 (1957)) using ether-free ditertiary butyl beryllium. More recently, a superior product has been obtained by the pyrolysis of diteritary butyl beryllium etherate dissolved in a high-boiling inert solvent (copending application Ser. No. 176,865, filed Feb. 26, 1962).

An object of this invention is the provision of a novel and improved method for the preparation of beryllium hydride. Another object of this invention is the provision of a method for the preparation of beryllium hydride which is characterized by simplicity and rapidity of operation. Still another object of this invention is the provision of a method for the preparation of beryllium hydride of a purity superior to that obtained by previously known methods. Other objects will appear hereinafter.

In accordance with the present invention, it has been found that beryllium hydride can be prepared conveniently and rapidly by pyrolyzing a beryllium dialkyl in the vapor phase at a pressure of from about 1 to about 45 millimeters of mercury absolute. Suitable beryllium dialkyls for use in this process contain from two to about five carbon atoms in each alkyl radical. The foregoing procedure represents an embodiment of the present invention.

Another embodiment of the present invention is the use of a carrier gas to facilitate the transfer of the beryllium dialkyl reactant from the reservoir to the pyrolysis chamber. A preferred embodiment of the present invention is the preparation of finely divided beryllium hydride by carrying out the above-mentioned vapor-phase pyrolysis under a pressure of from about to about 45 millimeters of mercury, absolute.

Still another embodiment is the preparation of vitreous beryllium hydride by carrying out the above-mentioned vapor-phase pyrolysis under a pressure of from about one to about four millimeters of mercury, absolute. Other embodiments will appear hereinafter.

The process of the present invention exhibits a number of distinct advantages over previously known methods for the preparation of beryllium hydride. Of particular significance is the high purity of the product obtained by the process of this invention. Purities previously reported were not appreciably in excess of 80 percent by weight whereas by the present process, purities of up to 86.5 percent by Weight have been obtained for the vitreous hydride and purities approaching 98 percent by weight for the finely divided material. Furthermore, since the process of this invention is carried out in the absence of a solvent, problems of solvent removal and solvent contamination of the product, which are characteristic of a number of the previously reported methods, are absent from the present process.

An apparatus suitable for carrying out the process of this invention comprises a reservoir for the beryllium di- 3,743,710 Patented July 3, 1973 ice alkyls connected through a flow meter to a pyrolysis chamber which, in turn, is connected through a collection chamber provided with a fine-mesh stainless steel screen (transverse to the direction of flow) to a Dry Ice trap and a vacuum pump in series. The pyrolysis and collection chambers together with the intermediate tubing are immersed in an oil bath. A manometer or other pressuremeasuring device is connected to the pyrolysis chamber. Stopcocks are provided for the purpose of isolating the various portions of the system when desired.

In conducting a run, the system is pumped out (to 0.005 mm. of mercury) with the beryllium dialkyl reservoir closed off from the rest of the equipment. The oil bath is then brought up to the desired temperature, after which the reservoir stopcock is opened to obtain the desired flow of the dialkyl beryllium vapor. A stopcock in the vacuum pump line is then adjusted to obtain the desired pressure. At the end of the run, the reservoir is again closed OE and the system pumped out. The decomposition and collection section is closed ofi by means of the stopcocks and removed to a nitrogen box, where it is opened and the solid products are removed.

In the pyrolysis chamber, the dialkyl beryllium vapor decomposes into two solid products, the relative proportions of which depend largely on the operating pressure, and a number of gaseous products. One solid product is the above-described vitreous material, which deposits on all surfaces in the pyrolysis chamber. The other is the finely divided powder, which is produced in the gas phase. This passes through the pyrolysis chamber and is collected on the screen in the collection chamber. The screen is installed at such a point in the exit line that, as indicated above, materials collected on it are continuously warmed by the same oil bath that warms the pyrolysis chamber.

Gaseous products are drawn through the screen, passed through a Dry Ice trap to remove condensables and exhausted from the system with a pump.

The invention will be more fully understood by reference to the following set of illustrative examples in which all parts and percentages are by weight.

EXAMPLE I Temperature of pyrolysis chamber (oil bath), 216 C.

Pressure in pyrolysis chamber, 17 to 45 mm. of mercury,

absolute.

Duration of run, minutes.

Vapor residence time in pyrolysis chamber, 0.5 to 2.3

minutes.

There was recovered from the collection screen a 62 percent yield (based on the ditertiary butyl beryllium fed) of dead white solids which, by gas evolution, analzyed 97.3 weight percent beryllium hydride and 0.0 weight percent beryllium metal.

The beryllium hydride was analyzed by reacting it with a mixture of deuterium chloride and deuterium oxide. The etfiuent gases from this reaction were led through a liquid nitrogen trap to remove condensable materials and then into a system for measuring the volume of noncondensable gas. The non-condensable gas was subsequently analyzed by the mass spectrometer to determine the relative amounts of HD and D The quantity of HD recovered was then proportional to the BeH content of the product material and the quantity of D was proportional to the beryllium metal content.

EXAMPLE II Temperature of pyrolsis chamber (oil bath), 231 C. Pressure in pyrolysis chamber, 17-34 mm. of mercury absolute. Duration of run, 45 minutes.

There was recovered from the exit screen a 56 percent yield (based on the ditertiary butyl beryllium fed) of white solids with a small amount of grey inclusions. Analysis by gas evolution: 97.7 weight percent beryllium hydride and 0.97 weight percent beryllium metal.

When the ditertiary butyl beryllium reactant of Example II is replaced by diethyl beryllium or by diisopropyl beryllium, similar results are obtained.

EXAMPLE III Temperature of pyrolysis chamber (oil bath), 245 C.

Pressure in pyrolysis chamber 27-43 mm. of mercury,

absolute.

Duration of run, 30 minutes.

The dialkyl beryllium reactant was ditertiary butyl beryllium. There was recovered from the exit screen a good yield of grey solids which, by gas evolution, analyzed 95.5 weight percent beryllium hydride and 1.4 weight percent beryllium metal.

When the ditertiary butyl beryllium reactant of Example III is replaced by di-normal butyl beryllium, similar results are obtained.

EXAMPLE IV Temperature of pyrolysis (oil bath), 180 C.

Pressure in p'yrolysis chamber, 19-39 mm. of mercury absolute.

Duration of run, 115 minutes.

There was recovered from the exit screen a 72 percent yield (based on the ditertiary butyl beryllium fed) of white solids which, by gas evolution, analyzed 85.7 weight percent beryllium hydrideand 0.85 weight percent beryllium metal. This run demonstrates the falling off in purity of the beryllium hydride product when the decomposition temperature is below the optimum range.

EXAMPLE V Temperature of pyrolysis chamber (oil bath), 260 C.

Pressure in pyrolysis chamber, 26-40 mm. of mercury absolute.

Duration of run, 65 minutes.

Average vapor residence time in pyrolysis chamber, 0.7

minute.

There was recovered from the exit screen a 38 percent yield (based on the ditertiary butyl beryllium fed) of a black solid which, by gas evolution, analyzed 18.8 weight percent beryllium hydride and 61.8 percent by Weight of beryllium metal. This run illustrates the sharp decrease in product purity at temperatures above the optimum operating range.

EXAMPLE VI In this experiment, purified hydrogen was used as a carrier gas. A proportion of the hydrogen was bubbled through the ditertiary butyl beryllium reservoir to entrain the organoberyllium vapor and this was then mixed with additional hydrogen to form the gas stream entering the pyrolysis chamber.

There was obtained a 6 3 percent yield (based on the ditertiary butyl beryllium fed) of white solids which, by gas evolution, analyzed 92.6 weight percent beryllium hydride and 0.0 weight percent beryllium metal.

When the ditertiary butyl ber'yllium reactant of Example VI is replaced by diisobutyl beryllium or by di-normalpropyl beryllium, similar results are obtained.

4 EXAMPLE v11 In this experiment, the pyrolysis chamber was packed with pieces of chemically pure anhydrous sodium chloride about inch on an edge to increase the surface area and thereby enhance the formation of vitreous product and to facilitate the separation of the latter.

Temperature of pyrolysis chamber (oil bath), 215 C.

Pressure in pyrolysis chamber, 1.1 mm. of mercury absolute.

Duration of run, 15 8 minutes.

Average vapor residence time in pyrolysis chamber, 0.007

minute.

After the run, one-half of the coated sodium chloride was leached with deoxygenated water in a nitrogen atmosphere. There remained thereafter a quantity of insoluble shiny black flakes. The yield based on the ditertiary butyl beryllium used was 23 percent. The flakes analyzed, by gas evolution, 8.6.5 weight percent beryllium hydride and 3.3 weight percent beryllium metal. No white powder was seen in the apparatus after the run. This experiment illustrates the preponderant formation of vitreous product at low system pressures.

When the anhydrous sodium chloride of Example VII is replaced by other anhydrous alkali metal halides, for example, potassium iodide, or by anhydrous alkaline earth metal halides, for example, barium bromide, similar re sults are obtained.

As indicated above, the original reactant or raw material employed in the process of this invention was a dialkyl beryllium compound wherein each of the alkyl groups contained from two to about five carbon atoms. Thus, in addition to the compounds mentioned above, the reactants may include di-normal butyl beryllium, diisoamyl beryllium, disecondary amyl beryllium, ditertiary amyl beryllium, and beryllium dialkyls containing unlike alkyl groups. The reaction temperatures employed in the process of the invention can range from about 180 C. or below to about 260 C. or above. However, temperatures below about 205 C. and temperatures above about 230 C. yield beryllium hydride of substantially decreased purity. Consequently, the range from 205 to 230 C. is preferred.

The reaction pressure can vary from less than one to more than 45 mm. of mercury absolute, but the character of the product varies markedly with the pressure. Extremely low pressures of up to about 4 mm. of mercury favor the formation of a vitreous or glassy variety of beryllium hydride, whereas pressures from about 5 to 45 mm. of mercury favor the formation of a white, fiufiy, powdery form of beryllium hydride. The vitreous form has a bulk density of about 0.71 gram per cc., whereas the bulk densit of the powder is less than 0.63 gram per cc. However, compression of the powder for 20' minutes under a pressure approaching 200,000 pounds per square inch and a temperature of C. increases its density to a value approximating that of the vitreous form.

As indicated in Example VI above, a carrier gas can be used, if desired, to facilitate the introduction of the dialkyl berylliumreactant into the pyrolysis chamber. The carrier gas, if used, should of course be inert with respect to the dialkyl beryllium reactant and the beryllium hydride product. Suitable carrier gases include: hydrogen, helium, neon, argon, krypton, xenon and gasesous parafiinic and olefinic hydrocarbons, such as methane, ethane, propane, butane, isobutane, ethylene, propylene, isobutene, butene-l and butene-2. Of these, hydrogen and the olefins corresponding to the particular beryllium dialkyl employed are preferred, the former because of its cheapness and availability and the latter because of its identity with one of the major decomposition products. When it is desired to obtain preponderantly the vitreous form of beryllium hydride, it is advantageous to pack the pyrolysis chamber with chunks of pure anhydrous alkali or alkaline earth metal halide, to increase the surface area. Of the various metal halides, sodium chloride is preferred for reasons of economy and availability.

The process of the invention can readily be made continous in operation by continuously introducing the reactants and withdrawing the product by means of screw conveyors or other suitable equipment. Such continuous operation has advantages both of economy and ease of control, and is therefore a preferred embodiment of the process of the invention.

When a carrier gas is not used, the reaction of this invention may be carried out in any atmosphere inert to both the reactant and the product, but dry nitrogen is preferred. Other suitable protective atmospheres include hydrogen, carbon monoxide, helium, neon, argon, krypton and xenon.

The product of this invention has strong reducing properties. The bulk of the product is insensitive to water and air, although a small amount of hydrolysis does occur upon contact with water. When heated in an inert atmosphere, the product is stable up to a temperature of about 250 C.

The beryllium hydride product of this invention is of great value as a fuel component of solid propellants. It also represents a convenient source of small storable quantities of hydrogen and of pure beryllium metal.

I claim:

1. Process for the preparation of beryllium hydride which comprises pyrolyzing, in the vapor phase and at a pressure from about 1 to about 45 millimeters of mercury absolute, a beryllium dialkyl, each of whose alkyl radicals contains from two to about five carbon atoms, and recovering the beryllium hydride product so formed.

2. The process of claim 1 wherein the pyrolysis temperature is in the range of from about 180 to about 260 C.

3.. The process of claim 1 wherein the pyrolysis temperature is within the range from about 205 to about 230 C.

4. The process of claim 1 wherein the vapor-phase, reduced-pressure pyrolysis is conducted on a continuous basis.

5. The process of claim 1 wherein a carrier gas is saturated with beryllium dialkyl by passing the gas through the liquid dialkyl and subsequently is introduced into the pyrolysis zone.

6. The process of claim 1 wherein dry nitrogen is saturated with beryllium dialkyl by passing said hydrogen through the liquid dialkyl and subsequently is introduced into the pyrolysis zone.

7. The process of claim 1 wherein a carrier gas comprising a hydrocarbon selected from the group consisting of dry gaseous paraffinic and monolefinic hydrocarbons is saturated with beryllium dialkyls by passing the gas through the liquid dialkyls and subsequently is introduced into the pyrolysis zone.

8. The process of claim 1 wherein dry isobutene is saturated with beryllium dialkyl by passing said isobutene through the liquid dialkyl and subsequently is introduced into the pyrolysis zone.

9. The process of claim 1 wherein the beryllium dialkyl is ditertiary butyl beryllium.

10. Process for the preparation of vitreous beryllium hydride which comprises pyrolyzing, in the vapor phase and under a pressure of from about one to about four millimeters of mercury absolute, a beryllium dialkyl each of whose alkyl radicals contains from two to about five carbon atoms and recovering the vitreous beryllium hydride product so formed.

11. Process for the preparation of vitreous beryllium hydride which comprises pyrolyzing, in the vapor phase under a pressure of from about one to about four millimeters of mercury absolute and in the presence of an anhydrous, water-soluble halide of an alkali metal or of an alkaline earth metal, a beryllium dialkyl each of whose alkyl radicals contains from two to about five carbon atoms and recovering the vitreous beryllium hydride product so formed.

12. The process of claim 11 wherein said halide is the anhydrous chloride of an alkali metal.

13. The process of claim 11 wherein said halide is sodium chloride.

14. Process for the preparation of finely divided beryllium hydride which comprises pyrolyzing, in the vapor phase and under a pressure of from about five to about 45 millimeters of mercury absolute, a beryllium dialkyl each of Whose alkyl radicals contains from two to about five carbon atoms and recovering the amorphous beryllium hydride product so formed.

References Cited UNITED STATES PATENTS 2,907,630 10/1959 Lawroski et al. 23-352 OTHER REFERENCES Head et al.: Journal of the American Chem. Soc., vol.

CARL D. QUARFORTH, Primary Examiner R. L. TATE, Assistant Examiner U.S. C1. X.R. 260-665 

